THE Water and Rivers Commission (WRC) is using "rules of thumb" to determine criteria for a Water Corporation application to pump 45 gigalitres of water a year from the South West Yarragadee aquifer to Perth's integrated water supply system.
This is despite a recent auditor general's report which said lack of scientific rigour was the reason why the WRC had not won any of the past 25 appeals against decisions to refuse further water allocations.
It said a precautionary approach to water allocation when scientific data was lacking could be appealed, leaving the way open for the Water Corporation to do the same if its application was turned down.
A new WRC document on the Yarragadee proposal, initially put out for a one-week public comment period but extended to February 6, outlines criteria of maximum acceptable environmental damage using rules of thumb.
They were also used to draw water from the Gnangara Mound systems, which had caused unforeseen environmental problems.
The accepted criteria or impact outlined in the matrix for the Blackwood River included a 50cm reduction in the river flow and 10pc increase in salinity, with this criteria based on observation and "limited data".
South West shires, including Busselton, Nannup, Augusta-Margaret River and Capel, oppose the 45gl application which led to the WRC's $8m year-long study, so far producing nearly 40 reports, studies, community updates and fact sheets.
Nannup shire president Barbara Dunnet said they were shocked to see the environmental damage the commission was prepared to accept in assessing the Water Corporation's 45gl application.
She said they were initially told there would be no environmental damage.
"The rules of thumb used for assessment in the Gnangara Mound were a total failure," she said.
"All the tress had to be cut on the mound and water allocations had to be cut back."
WRC will use a conceptual groundwater model, still under peer review, to determine how well the criteria will be met under seven different pumping scenarios, with and without the 45gl included.
The scenario that best meets the criteria would form the basis of the allocation limit and determine whether or not the corporation's application for 45gl would be approved.
Mrs Dunnet said the Whicher Water Resources Management Committee had to make its recommendations by February 20, however an independent hydrologist involved in the peer review was still unable to access some hydrology data from WRC.
She said there was a big concern that discharge from the Yarragadee aquifer into the Blackwood River would be reversed if the 45gl was taken out.
"I have not met one person who is in favour of the 45gl proposal," Mrs Dunnet said.
"There is no aquifer in the world that has been pumped sustainably."
The commission no longer proposes to take 45gl from one spot near the Blackwood River due to the expected impact on the river and has since broadened its wellfield options to include the Busselton-Capel groundwater area.
This area also includes internationally listed wetlands.
A total of nine bores over both regions could be used to provide the 45gl.
WRC south west project leader Dr Fionnuala Hannon said the best pumping scenario did not automatically mean acceptance of the 45gl application and that input to the recent document would help shape the commission's final decision.
"What the matrix says is that from all the studies, these are the values the South West community has said need to be taken into account when making a decision," she said.
Dr Hannon said the final model would be used for all water users across the board.
"I believe we have a responsibility to tackle these questions and decide where the line is drawn on what the acceptable impacts are," Dr Hannon said.
"Do we want to accept a 10pc increase in salinity in the Blackwood River?"
She said there was already an environmental impact from the 63gl currently being taken out of the South Yarragadee aquifer.
"No matter what we do, human beings will always impact on our environment," she said.
The WRC was expected to decide on the 45gl (45 billion litres) application next month, with Environment Minister Judy Edwards due to hand down a final decision in April.